1. Field of the Invention
The present invention relates to light-blocking devices and, more specifically, to a shield contoured for use with mammogram x-ray films, where the shield is used to block light transmission of lighter areas on the film to promote better viewing of darker areas on the film.
2. Description of the Invention Art
Radiological techniques, especially x-rays, exist as effective and reliable diagnostic tools having a wide range of medical applications. Mammography is one such application where x-ray photographic films of the breasts are taken for interpretive analysis and diagnosis of possible disease or abnormalities. Specifically, the process involves exposing a piece of film to x-rays that have been passed through the tissues of the breast. The different kinds of breast tissue have different affinities for the x-ray radiation, and therefore absorb different amounts of the x-ray radiation. When the x-rays pass through the breast tissues and expose the film, the degree of exposure, or darkness, is proportional to the amount of radiation absorbed by the different breast tissues. The resulting image, or mammogram, produced yields important information regarding the presence or absence of breast cancer, which may selectively absorb more radiation than normal breast tissues.
Two views of the breasts are typically obtained during an examination. The craniocaudal view provides a view of each breast from above, or a "bird's eye" view. The mediolateral oblique view provides a side, profile view of each breast. A physician or radiologist views the films by placing them on a viewbox, where fluorescent light shines through the film to the examiner's eyes. Depending on the density of the object between the x-ray source and the film, which varies with the tissue types present in the breast, various features of breast disease can be recognized. Often, films of the right and left breast are hung "back-to-back." This arrangement facilitates disease recognition, as both breasts are relatively symmetrical and any difference therebetween can be detected and assessed as a possible abnormality.
On mammograms cancers typically appear as stellate masses with spiculated margins, but they may also appear as clusters of microcalcifications, with or without a stellate mass. It may sometimes be difficult to distinguish a tumor from a benign cyst, which may appear as a mass with a smooth border, or with benign fibroadenomas, which may contain dense popcorn-like calcifications, or with lymph nodes. Mammograms are difficult to interpret, and may be double read (read independently by two different radiologists). While a negative mammogram cannot rule out breast cancer, a properly read mammogram can detect a cancer when it is very small, even before they can be detected by palpation.
A problem arises when the physician or radiologist hangs the mammogram film on the viewbox. Areas of excessive photographic contrast occur throughout the mammogram film. While the areas representing the subcutaneous and retroglandular tissues are darker (more radiolucent), the glandular and axilla areas are lighter (more radiopaque). Evaluation of dark areas next to light areas is very difficult, as the pupil adjusts to the light areas and thereby makes accurate visualization of the dark areas difficult, time-confusing and frustrating for the physician or radiologist.
Unsatisfactory solutions to this problem have included removing the films from the viewbox to hold them up to brighter light and using a make-shift shield, such a medical chart or a writing tablet, to cover the lighter parts of the film. Such tactics are further complicated by uneven room lighting or by the disparity between the straight edges of the object used as a make-shift shield and the contoured x-ray pattern generated by the different breast tissues. Also, these methods have an unprofessional appearance which may be of medical concern to a patient, especially in unclear cases, where an accurate reading of the mammogram films is critical.
U.S. Pat. No. 2,227,944 discloses an anti-glare shield adapted for viewing x-ray films. The shield comprises a pair of connected complementary shield elements, each having a handle and defining a vision opening. These shield elements are pivotally assembled with means for urging them into a position in which the vision openings are in alignment, so as to isolate a specific area on the film from those surrounding it, and to enable a physician to better examine that area. While useful with orthopedic- and vascular-related x-ray films, the device of '944, with its vision openings, lacks the contoured shape necessary for examination of mammogram films. The device requires time to adjust the opening to a convenient viewing size, and the vision opening is too small to simultaneously view areas along the sweeping contour of the breast. Furthermore, the small vision openings of the device of '944 do not provide a sufficient area for the examiner to compare the right and left breasts, as required to check for non-symmetrical irregularities that would indicate disease. In this sense, the device of '944 does not work with mammogram films.
Other less relevant inventions and patents include the vehicle anti-glare shield of U.S. Pat. No. 3,857,630, the nonreflective articles of U.S. Pat. No. 5,212,596, the automobile glare shield of U.S. Pat. No. 5,247,391, the computer monitor shield of U.S. Pat. No. 5,369,332 and the book shade apparatus of U.S. Pat. No. 5,543,967. Also of limited relevance to the present invention are the goggle lenses of U.S. Pat. No. 3,791,722, the optical instrument training device of U.S. Pat. No. 4,059,347 and the welding face guard of British Patent No. 533,496.
Given the shortcomings of the above inventions and patents, there is a need for a device that facilitates accurate reading of mammogram films. There is also a need for a device that eliminates the contrast created by lighter portions of the mammogram x-ray film so that an examiner can better view the darker portions. There is a further need for a device that has a contoured shape to better fit the contoured x-ray pattern generated by the different breast tissues. There is still a further need for a film-viewing aid that allows comparative bilateral image assessment in mammogram films of right and left breasts for detection of unsymmetrical irregularities.
None of the above inventions and patents, taken either singly or in combination, is seen to describe the instant invention as claimed.